Correspondence

Iodine Content of Prenatal Multivitamins in the United States

N Engl J Med 2009; 360:939-940February 26, 2009

Article

To the Editor:

Normal thyroid function in fetuses and breast-fed infants, which is dependent on sufficient maternal dietary intake of iodine, is crucial for normal neurocognitive development.1 Children of mothers with severe iodine deficiency may have cretinism. Iodine deficiency affects more than 2.2 billion persons (38% of the world's population) and is the leading cause of preventable mental retardation worldwide.2 Even mild iodine deficiency may have adverse effects on the cognitive function of children.1

National surveys including the first and third National Health and Nutrition Examination Surveys (NHANES I and III) and NHANES 2001–2002 have reported a decrease of approximately 50% in adult urinary iodine values since the 1970s in the United States. In the subgroup of women of childbearing age, the median urinary iodine value decreased from 294 to 128 μg per liter. The most recent NHANES survey (2003–2004) reported that 37.2% of this subgroup of women had urinary iodine values below 100 μg per liter, which suggests mild iodine deficiency.3

The Institute of Medicine recommends a daily iodine intake of 220 μg during pregnancy and 290 μg during lactation; the World Health Organization recommends 250 μg of iodine daily for pregnant and lactating women. The American Thyroid Association has recommended that women receive prenatal vitamins containing 150 μg of iodine daily during pregnancy and lactation.4 However, the iodine content of prenatal multivitamins is not mandated in the United States.

Using the Internet, we identified 127 nonprescription and 96 prescription prenatal multivitamins currently marketed in the United States. Of these multivitamins, 114 (87 nonprescription and 27 prescription) contained iodine; according to the product labeling, 101 (89%) contained 150 μg or more of iodine per daily dose. The iodine was in the form of kelp (in 42 multivitamins), potassium iodide (in 67), or another ingredient (in 5).

We measured the iodine content in 60 randomly selected iodine-containing prenatal multivitamins (1 to 2 tablets per bottle, each from a single lot) and compared the results with the values on their labels (Table 1Table 1Iodine Content in Prenatal Multivitamins.). The mean (±SE) level of measured iodine per daily dose in 35 potassium iodide–containing vitamins was 119.0±13.6 μg. Potassium iodide contains 76% iodide. Thus, the measured iodine content was approximately equivalent to 76% of the total potassium iodide content. The measured iodine in 25 brands containing kelp was 33 to 610 μg per daily dose. Thirteen brands contained levels of iodine that were discordant by 50% or more with the values on their labels, including 10 brands with iodine values that were lower by 50% or more. Variations in the iodine content of kelp have been reported previously.5

Manufacturers of prenatal multivitamins in the United States should be encouraged to use only potassium iodide, to maintain consistency in labeling, and to ensure that these vitamins contain 150 μg of supplemental daily iodine by including at least 197 μg of potassium iodide per daily dose, as recommended by the American Thyroid Association.

Angela M. Leung, M.D.
Elizabeth N. Pearce, M.D.
Lewis E. Braverman, M.D.
Boston University Medical Center, Boston, MA 02118
elizabeth.pearce@bmc.org

5 References

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   Iodine deficiency. Ottawa: International Council for the Control of Iodine Deficiency Disorders. (Accessed February 5, 2009, at http://www.iccidd.org/pages/iodine-deficiency.php.)
   

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Citing Articles (11)

Citing Articles

1. 1

   Angela M. Leung, Elizabeth N. Pearce, Lewis E. Braverman. (2011) Iodine Nutrition in Pregnancy and Lactation. Endocrinology & Metabolism Clinics of North America 40:4, 765-777
   CrossRef

2. 2

   Alex Stagnaro-Green, Marcos Abalovich, Erik Alexander, Fereidoun Azizi, Jorge Mestman, Roberto Negro, Angelita Nixon, Elizabeth N. Pearce, Offie P. Soldin, Scott Sullivan, Wilmar Wiersinga. (2011) Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum. Thyroid 21:10, 1081-1125
   CrossRef

3. 3

   R. L. Brent. (2011) The Role of the Pediatrician in Preventing Congenital Malformations. Pediatrics in Review 32:10, 411-422
   CrossRef

4. 4

   CHRISTINA D. YARRINGTON, ELIZABETH N. PEARCE. (2011) Dietary Iodine in Pregnancy and Postpartum. Clinical Obstetrics and Gynecology 54:3, 459-470
   CrossRef

5. 5

   Christina Yarrington, Elizabeth N. Pearce. (2011) Iodine and Pregnancy. Journal of Thyroid Research 2011, 1-8
   CrossRef

6. 6

   Piedad Santiago, María Berrio, Pablo Olmedo, Inés Velasco, Baltasar Sánchez, Eduardo García, Julia Martínez, Federico Soriguer. (2011) Reference values for thyroid hormones in the population of pregnant women in Jaen (Spain). Endocrinología y Nutrición (English Edition) 58:2, 62-67
   CrossRef

7. 7

   Bruce Rosenzweig. 2010. Kelp and Thyroid Function. , 125-134.
   CrossRef

8. 8

   Angela Leung, Elizabeth N Pearce, Lewis E Braverman. (2010) Role of iodine in thyroid physiology. Expert Review of Endocrinology & Metabolism 5:4, 593-602
   CrossRef

9. 9

   Paula R Trumbo. (2010) Perchlorate consumption, iodine status, and thyroid function. Nutrition Reviews 68:1, 62-66
   CrossRef

10. 10

    Cria O. Gregory, Mary K. Serdula, Kevin M. Sullivan. (2009) Use of Supplements with and without Iodine in Women of Childbearing Age in the United States. Thyroid 19:9, 1019-1020
    CrossRef

11. 11

    (2009) More on Iodine Content of Prenatal Vitamins. New England Journal of Medicine 360:24, 2582-2583
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